Field of the Invention
The invention lies in the field of fluid dynamics. In particular, the invention pertains to airfoil and wing designs.
The primary aerodynamic principle utilized in so-called heavier-than-air craft is the effect of the dynamic pressure of air acting on the craft as it is being propelled through the air. The dynamic pressure is proportional to the relative speed between the air and the aircraft. Crude air resistance acting on poor aerodynamic shapes translates into drag, which is defined as the force counteracting the forward thrust force of the aircraft. A certain amount of drag cannot be avoided. However, the drag force can be minimized by the proper design of airfoils and fuselage shapes. The object is to minimize drag and to maximize lift, i.e., to optimize the lift-to-drag ratio.
Early wing designs were based on the understanding that lift is obtained by a vertical force component acting upward, from below, on the wing. It was found that a thin plate with a very narrow attack surface and a slight downward curve (camber) provided a sufficient amount of lift. In other words, the pitch angle of the forward-most portion of the plate was approximately zero relative to the forward velocity vector of the translational movement of the aircraft and the wing had a downward curve by a few degrees. These types of wings were used in the early mono and biplanes. With the relatively low speeds of those early planes, the thin, slightly curved shape of the wing was acceptable. As the speeds increased, however, the lift-to-drag ratio very quickly deteriorated. The drag, it was found, was caused by the turbulent flow, i.e., the vortices or eddies, at the trailing edge of the wing.
In addition to the wing drag problem, the aerodynamic efficiency of an aircraft also includes factors such as the fuselage shape, all exposed surfaces, and other non-smooth protruding shapes. Drag is also affected by micro-friction between the exposed surfaces and the innermost layer (flow sheet) of the fluid impinging and being deflected by the surfaces. The total drag force on the aircraft is the sum of all drag vectors. The lift component, on the other hand, is largely provided only by the wings of the craft. This invention is primarily concerned with improving the lift-to-drag ratio of those structures.
Only after the early aircraft designers recognized that most of the lift on a wing in fact is due to the vacuum effect above the wing (the negative pressure compensates for the fluid compression forward of and below the wing)--the typical ratio is that approximately two-thirds of the lift originates from the upper vacuum effect and one-third is due to the compression below the wing--they started to more closely examine the upper surface of wing. This resulted in the development of the airfoil. The airfoil shape at first glance appears counter-intuitive. The airfoil has a thickened forward section which tapers to a very thin tip structure at the trailing edge. The basic airfoil design was further developed with a flap at the trailing edge, with which the early downward camber can be modeled. Also, a slot at the leading edge of the airfoil, which allowed a partial pressure below the wing to flow to the upper surface of the airfoil, was found to substantially reduce the formation of vortices and thus added drag forces.
The airfoil, with various developments and improvements within the basic principle, is currently the most-used wing shape of low to mid-speed (sub-Mach) aircraft.
These above-described principles concerning vortice creation and drag are similarly applicable to propellers and rotor blades. Furthermore, the principles concerning aircraft propellers are also extendible to watercraft. There, the eddie formation principles applicable to the relatively thin fluid air find their equivalents in the denser fluid water with the formation of eddie current vortices, cavitation, and super-cavitation. Those structures are the subject of my copending applications (attorney docket Nos. F-7759 and F-7760), based on the same international priority application.